Basic Trope: A character has brown skin, and the viewers do not know his ethnicity.
Straight: Bob is brown-skinned, and his ethnic background is not disclosed.
Exaggerated: Bob has traits that could define him as a mixture of black, white, Native American, East Asian, South Asian, Southeast Asian, Central Asian, Middle Eastern, Antarctican and any other race.
Downplayed: Bob is dark-skinned, and considered "black", but his appearance may suggest that there are other ethnicities in his racial background.
Parodied: Bob is the subject of a Game Show where contestants try to guess his race.
Zig Zagged: Bob is brown skinned and of unclear ethnicity then it is revealed he has Filipino parents. However he is adopted. He reunites with his birth mother who is a tanned Caucasian - however she was just the invitro carrier. The trail goes cold from there. At least until they get involved with genetic analysis....
Averted: Bob's race is disclosed.
Enforced: A sketch comedy show hires brown actors because they can play celebrities of various ethnicities.
Lampshaded: "Out of curiosity, do you guys know what Bob's ethnicity is?"
Invoked: Bob thinks his ethnic background should not change the way people treat him, so he never discloses it to anyone.
Exploited: Bob uses his ambiguous appearance in order to infiltrate an ethnic enclave composed of people of a specific brown-skinned race.
Defied: "Hi, my name is Bob, and before you start making speculations about my race, I'd like to clarify that I'm 1/4 black, 1/4 white and 1/2 Native American."
Deconstructed: All of his life, Bob has been assumed by strangers as being of various races. When he corrects them, their reply is always "Whatever". These situations made him understand what it's like to experience racism against multiple ethnicities.
Reconstructed: These strangers made a fool of themselves by associating Bob with the wrong race. They learn the hard way not to be racist.
Played For Laughs: Trying to find Bob's ethnicity becomes a Running Gag, and to add some Hypocritical Humor to the mix, Bob wonders what ethnicity Alice is.
Played For Drama: Bob is born in segregation era America, where he's been targeted for his tanned appearance. To make matters worse, the minorities are uncomfortable with him for not sharing the same resemblances.